The proposed research can be divided into three categories: 1) Improvements in the design and fabrication of the existing total heart replacement device: The design will be modified to allow increased maximum cardiac output to approximately 15 l/min without any appreciable increase in size. A new polyether-type polyurethane will be employed to fabricate the new heart. 2) Critical evaluation of the performance and durability of the prosthesis and newly designed control-driving unit by in vitro and in vivo testing: The heart powered by the new control and driving unit will be tested extensively in our two new mock-circulatory systems. Following this evaluation, in vivo testing of the combination will be performed. 3) Pathophysiological evaluation of total artificial heart pumping: Major emphasis will be given to studies designed to pinpoint problems in various systems. Examples are, respiratory distress, fluid balance problems, response of the prosthesis and circulatory system to moderate exercise, such as standing, and adequate tissue and organ perfusion. Test and reevaluation of cardiovascular drugs will be performed.